1. Field of the Invention
The present invention relates to an optical touch panel and a method of detecting touch point positions on an optical touch panel, more particularly to an optical touch panel and a method of detecting multiple touch point positions on an optical touch panel.
2. Description of the Related Art
Referring to FIG. 1, a conventional optical touch panel 1 includes a support 11 defining a surface 111, light sources 12, a pair of optical detectors 13, and a processing unit 14. Each of the optical detectors 13 is configured to output a signal indicating intensities of light detected thereby. The processing unit 14 is operable, according to the signals from the optical detectors 13, to compute coordinates of at least one touch point 10 on the surface 111 of the support 11 using trigonometric functions. However, a value of the trigonometric functions with respect to an angle is approximate to 0 or infinity when the angle is approximate to 0 degree. Accordingly, when a position of the touch point 10 on the surface 111 is close to an upper-right corner or an upper-left corner, angles α and β of the touch point 10 with respect to the respective optical detectors 13 are approximate to 0 degree such that values of the trigonometric functions with respect to the angles α and β are approximate to 0 or infinity and coordinates of the touch point 10 thus computed are relatively inaccurate. Further, when there are a plurality of touch points on the surface 111, it is hard to determine that the coordinates thus computed correspond to a real touch point or to a ghost point.
U.S. Pat. No. 5,317,140 discloses a system and a method for optically determining the direction of an object within a generally planar viewing field. The system includes a pair of cameras positioned at upper corners, and an optional central camera to improve resolution near an upper middle region of the viewing field. However, this patent fails to provide a solution for determining a ghost point.